Large scale metal forming

ABSTRACT

In certain embodiments described herein, a heated line forming system includes a heating coil system configured to produce a heated line on a surface of a metal part. The heated line forming system also includes an air knife cooling system configured to maintain a dry area for the heated line, and to direct a coolant (e.g., cooling water, liquified gases such as liquid argon, solidified gases such as carbon dioxide snow, and so forth) around the heated line via a spray mechanism such that the coolant does not flow or splash into the heated line on the metal part. In certain embodiments, the heated line forming system includes multiple induction coils arranged along a line and spaced a short distance apart, but which, when operated simultaneously together, form a heated line on a surface of a metal part.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from and the benefit of U.S.Provisional Application Ser. No. 61/901,294, entitled “LARGE SCALE METALFORMING,” filed Nov. 7, 2013, which is hereby incorporated by referencein its entirety for all purposes.

BACKGROUND

The invention relates generally to metal forming, and more particularly,to automated thermal forming processes and systems.

Steel and, to a lesser extent, aluminum are the structural materials ofchoice for most fabricating. Consequently, metal bending and metalforming operations will continue to be of significant importance tofabricators. As quality and productivity requirements increase,automated systems will be required to meet those demands. Today, thefabricating industry depends on manual processes, such as line heating,spot heating, mechanical bending, press brakes, and manually operatedequipment for most metal forming operations. One major fabricatingindustry is the shipbuilding industry; consequently, shipbuildingexamples are included in this description. However, other fabricatingindustries will benefit from the automated thermal forming processes andsystems described herein.

BRIEF DESCRIPTION

In general, two methods are used in forming large metal plate pieces:hot forming and cold forming. Mechanical cold forming is generallyaccomplished using a linear press or a roller, and is mainly used as amethod to form simple curved plates or non-complex three dimensionalshaped plates or to produce plates with constant curvature as apreceding method for forming plates where there is curvature in both thex and y perpendicular axes in the plane of the originally flat platesurface. These doubly curved plates generally use hot forming. Hotforming can be accomplished using a press to apply force on a uniformlyheated plate. Another hot forming method, which may be referred to asthermal forming or line heating, uses residual thermal elastic-plasticdeformation, which is created by differential or local heating andcooling, but where no externally applied force is used. This lineheating or thermal forming may be used to form doubly curved plates oras a method to remove residual welding deformation in ship blocks.

The hot forming method may be referred to as a line heating processsince plates are heated by moving a single heat source in a constantdirection along a line, or a virtual line, on the plate surface. A largeflat metal plate may be formed to have a three-dimensional shape ofcompound curvature by locally heating a spot to an elevated temperaturethat is then moved along predetermined lines and then quickly cooling.The heating may or may not extend completely through the thickness ofthe plate. The use of through thickness heating and then cooling maycause significant shrinkage in-plate, a significant portion of which isin a direction perpendicular to the line of heating being traversed bythe heat source or heated spot. Heating may be carried out along linesin a geometric pattern and in a preselected sequence such that the platehas a gradual transformation to a new shape. The plate can be supportedupon an underlying cradle, or a series of pin-jigs, which may be in theshape of the finished plate, or adjusted during the forming process.

In certain embodiments described herein, a heated line forming systemincludes a heating coil system configured to produce a heated line on asurface of a metal part. The heated line forming system also includes anair knife cooling system configured to maintain a dry area for theheated line, and to direct a coolant (e.g., cooling water, liquifiedgases such as liquid argon, solidified gases such as carbon dioxidesnow, and so forth) around the heated line via a spray mechanism suchthat the coolant does not flow or splash into the heated line on themetal part. In certain embodiments, the heated line forming systemincludes multiple induction coils arranged along a line and spaced ashort distance apart, but which, when operated simultaneously together,form a heated line on a surface of a metal part.

DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 illustrates a typical linear press brake that may be used withconventional metal forming processes;

FIGS. 2A through 2C illustrate multiple steps in an exemplary thermalforming process in accordance with embodiments of the presentdisclosure;

FIG. 3 is a diagram of angular distortion in butt welds in accordancewith embodiments of the present disclosure;

FIGS. 4A and 4B illustrate the time and temperature differences ofoxy-acetylene heating versus induction heating, respectively;

FIG. 5 is a side view of an exemplary automated thermal forming systemin accordance with embodiments of the present disclosure;

FIG. 6 is another side view showing a relatively complex bend beingformed in accordance with embodiments of the present disclosure;

FIGS. 7A and 7B are top view of a line heating method versus a heatedline method for metal bending or forming in accordance with embodimentsof the present disclosure;

FIG. 8 is a cross-sectional side view of an exemplary thermal formingsystem in accordance with embodiments of the present disclosure;

FIG. 9 is a side view of an exemplary heating bed comprising adeformable liquid-filled bladder upon which plates may be supportedduring a thermal forming process in accordance with embodiments of thepresent disclosure; and

FIG. 10 is a cutaway top view of exemplary thermal forming assemblieshaving air guides with opposite parallel walls disposed on oppositesides of a heating head in accordance with embodiments of the presentdisclosure.

DETAILED DESCRIPTION

One or more specific embodiments of the present invention will bedescribed below. In an effort to provide a concise description of theseembodiments, all features of an actual implementation may not bedescribed in the specification. It should be appreciated that in thedevelopment of any such actual implementation, as in any engineering ordesign project, numerous implementation-specific decisions must be madeto achieve the developers' specific goals, such as compliance withsystem-related and business-related constraints, which may vary from oneimplementation to another. Moreover, it should be appreciated that sucha development effort might be complex and time consuming, but wouldnevertheless be a routine undertaking of design, fabrication, andmanufacture for those of ordinary skill having the benefit of thisdisclosure.

When introducing elements of various embodiments of the presentinvention, the articles “a,” “an,” “the,” and “said” are intended tomean that there are one or more of the elements. The terms “comprising,”“including,” and “having” are intended to be inclusive and mean thatthere may be additional elements other than the listed elements.

The cost of using the manual and manually operated metal formingprocesses discussed above may be significant. FIG. 1 illustrates atypical linear press brake 10 (e.g., a 40 foot wide, 2,500 ton pressbrake) that may be used with conventional metal forming processes. Thepress brake 10 can make a bend relatively quickly, but for anysignificant size part, the system requires a crane 12 to lift the sheetmaterial 14 and as many as five crane and machine personnel 16 workingfor several minutes before the bend can be produced. Sometimes, thecrane 12 may be replaced with a semi-automated plate moving system(which can be relatively expensive). In order to maintain reasonablesalary levels for shipyard employees and still compete on aninternational level, metal forming in the shipyard may benefit from moreautomated methods.

The existing manual workforce in the fabricating industry has largelybeen replaced with workers that oversee and maintain computerizedmonitoring systems and control systems, and many of the processes thatwere once used, are no longer being applied. For example, two decadesago, most holes were drilled using rotating drills. Today, in automatedfactories, holes are drilled with lasers.

One reason why fabricating has been unable to implement automation inthe Unites States and Europe is the general nature of fabricating. Massproduced ships, produced elsewhere, such as in Asia, are highlyautomated, but those shipbuilders depend on careful robot programmingfor much of their process control and quality monitoring. This is alsotrue of the automobile industry, particularly in the United States andelsewhere. The commonality is production of large quantities ofidentical components. Shipbuilding in the United States and, to anextent, in Europe, has a large component of one-off and few-of-a-kindproduction. In these environments, robot programming and re-programmingfor many different kinds of parts can be prohibitively expensive, forexample, up to or in excess of billions of dollars for some automobileplants.

In order for fully automated metal forming to be economically viable, itwould be advantageous to utilize flexible automation in the one-off andfew-of-a-kind manufacturing environment of shipbuilding. Flexibleautomation is generally based on the ability to accomplish three tasksautomatically: 1) program robot motion and process control directly frominformation contained in computer-aided design (CAD) models; 2) have newmetal forming processes that are capable of flexible automation; and 3)monitor for quality assurance, and control processes—all in real-time.

Thermal forming of metals is generally a process of creating residualstrain in a metal part by differential heating and cooling. Thisprocess, as used today in shipyards, is called “line heating,” which isprimarily done manually by relatively highly skilled individuals. Theembodiments described herein are directed toward automated thermalforming processes and systems that are relatively fast, and can producethermally formed parts with greater accuracy than line heating andconventional metal forming operations, such as the linear brake press 10illustrated in FIG. 1.

FIGS. 2A through 2C illustrate multiple steps in an exemplary thermalforming process 18 in accordance with embodiments of the presentdisclosure. The illustrated thermal forming process 18 includes twoprimary steps, heating and cooling, that form the metal withoutrequiring externally applied forces. As illustrated in FIG. 2A, theprocess 18 may begin with undeformed sheet material 14. Then, asillustrated in FIG. 2B, heating may be applied to the sheet material 14,for example, by moving a heat source 20 (e.g., a flame, a laser beam, aninduction heating coil, and so forth) across a first surface 22 of thesheet material 14. The temperature of the metal of the sheet material 14at the heated region 24 is increased sufficiently such that sufficientthermal expansion causes plastic deformation to result. It is noted thatthe heated region 24 on the first surface 22 does not expand to thesides. Rather, it is constrained by the relatively cold surroundingmaterial, so that it expands away from the first surface 22, permanentlydeforming—getting thicker. As illustrated in FIG. 2C, once the sheetmaterial 14 cools, the heated/deformed region 24 shrinks, as illustratedby arrows 26, pulling on the first surface 22 of the sheet material 14.The heated region 24 of the sheet material 14 is cooled back to ambienttemperature, which causes thermal shrinking that results in shrinkagestresses, that are sufficient to generate strain and cause bending(e.g., deformation) in the sheet material 14. In certain embodiments,this process may be repeated by scanning the heat source 20 across thefirst surface 22 of the sheet material 14, pipe material, I-beammaterial, L-shaped material, bar stock, conical, circular, trapezoid,square, polygon, or other initial shape, in a predefined pattern tocreate desired shape.

The theory of the thermal forming process is that the heating operationhas to produce thermal expansion, and permanent strain, in thethrough-thickness direction 28 (i.e., a direction generallyperpendicular to the first surface 22 of the sheet material 14). Thecooling operation needs to produce thermal shrinkage and permanentstrain in the two-dimensional plane 30 that is perpendicular to thethrough-thickness direction 28 (i.e., the two-dimensional planegenerally parallel to the first surface 22 of the sheet material 14). Itis this asymmetry of plastic deformation due to thermal expansion andshrinkage that causes the metal to bend.

In general, relatively quick heating of the sheet material 14 isadvantageous insofar as thermal expansion of the heated metal benefitsfrom being constrained to be only in the through-thickness direction 28.As such, the heating should be done fast enough to get a significantamount of the metal heated, but only heated about halfway through thethickness of the sheet material 14, as illustrated in FIG. 2B. Thisfacilitates the thermal expansion occurring primarily in thethrough-thickness direction 28 because the heat has not spread to thesurrounding material, if it is heated quickly. The yield strength of thehot metal is relatively low so that it easily deforms, constrained bythe higher yield strength cold metal. However, the thermal shrinkagethat occurs will, to some extent, be in the plane 30 that is parallel tothe metal surface 22, and primarily concentrated near one surface (e.g.,the first surface 22 in the embodiment illustrated in FIG. 2C). Thepreviously heated metal cools and the yield strength increases,consequently this metal will exert a significant load on the surroundingmetal and cause the metal part to bend.

As such, for the cooling operation, the primary thermal shrinkage isgenerally in the plane 30 perpendicular to the through-thicknessdirection 28, and concentrated close to one of the first surface 22 orthe second surface 32 of the sheet material 14 (e.g., again, the firstsurface 22 in the embodiment illustrated in FIG. 2C). FIG. 3 is adiagram of angular distortion in butt welds in accordance withembodiments of the present disclosure. The thermal forming processgenerates bending of the metal in welds, such as the butt weld 34illustrated in FIG. 3, much the same way as the solid sheet material 14of FIGS. 2A through 2C. If the primary thermal shrinkage is in the plane30 perpendicular to the through-thickness direction 28, and the sheetmaterial 14 is hotter on one surface 22, 32 than the other surface 22,32, then bending will occur. In general, the bending will be toward thehottest surface 22, 32.

Precise control of the heating for the thermal forming process describedherein facilitates proper metal forming. In general, if the heat is notproperly controlled, then the process will not lead to desired metalforming. There are several considerations with respect to such heatcontrol. First, the heated material 14 should be constrained by asurrounding “container” of cold metal. In general, the heat should beconstrained to only the material closest to the surface which is beingheated (e.g., the first surface 22 in the embodiment illustrated in FIG.2B) so that the maximum shrinkage will occur concentrated at or nearthat surface. Also, in general, the surface of the material on the otherside of the plane 30 perpendicular to the through-thickness direction 28(e.g., the second surface 32 in the embodiment illustrated in FIG. 2B)and mid-way through the thickness of the metal does not receive anysignificant heating. Since heat flow (i.e., conduction) to thenon-heated side of the metal is time-dependent, this means that the heatshould be applied at the fastest possible rate, to maximize the thermalgradient in the through-thickness direction 28 at the time when theheating is stopped and cooling begins. In general, thermal expansion inthe plane 30 that is perpendicular to the through-thickness direction 28will be counterproductive to obtaining the maximum efficiency of themetal forming process. As such, the surrounding material may be keptrelatively as cold as possible to constrain the heated material. Thisgenerally insures that the primary thermal expansion will be in thethrough-thickness direction 28. Otherwise, the net amount of thermalcontraction that causes the bending will be reduced by the amount ofthermal expansion that is not in the through-thickness direction 28.

Flame heating is the primary method applied in most shipyards. Laserheating is another potential heat source 20 for thermal forming, butneither flame or laser heating is ideal for use on thicker metal. Flameheating has the drawback that most of the heat that is produced by thecombustion process is lost to the surrounding environment (e.g., as muchas 30%-50% of the flame heat may be lost). In addition, heat that isexternally generated must pass through the interface at the surface ofthe metal, which is an additional inefficiency, both of flame heating,as well as laser heating. Moreover, the heating efficiency of a lasercan be even less efficient than a flame. First, lasers typically operateat an efficiency of 3% to 30%. So, even for an efficient laser, 70% ofthe energy may be lost as waste heat. In addition, an associatedrefrigeration system that removes the waste heat uses energy as well.Then, before the heat can pass through the interface of the metalsurface, the laser must couple with the surface to transfer the energyof the laser light beam. As such, although flame heating and laserheating may definitely be used with the thermal forming embodimentsdescribed herein, for both flame and laser, the energy efficiency may bebelow 30%.

Consequently, meeting the first objective of the thermal forming system,to heat as quickly as possible, while both flame and laser heating canbe used, they can be far from optimum. To heat as quickly as possible,the system should be able to put the maximum amount of heat into theinterior of the heated material 14 in the shortest amount of time. Incertain embodiments, induction heating may be used to generate inducedelectric current directly in the part, near the surface closest to aninduction coil. Heating may be accomplished by high frequency “eddy”currents being conducted in the interior bulk of the material 14, drivenby a high-frequency electromagnetic field created by the induction coil.In general, induction heating may be the fastest and most efficientheating method for use with the embodiments described herein. Examplesof induction heating systems that may be utilized in the embodimentsdescribed herein are disclosed, for example, in U.S. Patent ApplicationPublication No. 2011/0284527, entitled “Auxiliary welding heatingsystem”, filed May 19, 2011, which is incorporated by reference herein.

The calculation of time to reach forming temperature depends on the heatflux of the chosen process. In certain situations, for example, themaximum allowable temperature for thermal forming for EH-36 marine steelis approximately 1150° F. The following equation can be used tocalculate the relative time required to reach the forming temperature.

$t_{ig} \propto \left\lbrack \frac{T_{ig} - T_{o}}{q^{n}} \right\rbrack^{2}$t_(ig) = Time  to  reach  forming  temperature, T_(ig) = Forming  Temperature (^(∘)  K),  = 1150T₀ = Ambient  Temperature(^(∘)  K),  = 370 $\begin{matrix}{q^{''} = {{Heat}\mspace{14mu}{{flux}\left( {W\text{/}m^{2}} \right)}}} \\{= {48,880,000({acetylene})}} \\{= {1,400,000,000\left( {35\mspace{20mu}{kW}\mspace{14mu}{induction}} \right)}}\end{matrix}$

Because of the variability of heat generation efficiency, and thethermal barrier of the metal surface, only an approximation of therelative time may be reached. However, as but one example, experimentaldata comparing a number 4 Oxy-acetylene torch tip to a 35 kW inductionheating head shows that the ratio of the heating time is approximately20:1.

-   -   t_(ig)=20 sec. (acetylene)    -   t_(ig)<1 sec. (35 kW induction)

FIGS. 4A and 4B illustrate the time and temperature differences ofoxy-acetylene heating versus induction heating (e.g., with a 35 kWinduction heating system), respectively. After approximately sixseconds, the heated region 24 of the flame 36 has extended well beyondthe half thickness point of the material 14 and is spreading well beyondthe width of the required heated spot size, yet the maximum temperatureat the first surface 22 is still only 800° F. In contrast, thetemperature of the heated surface 22 after only approximately one secondwith induction heating has exceeded the 1150° F. thermal formingtemperature. Therefore, the induction controller needs to only heatapproximately 850 ms. at full power, to achieve the desired formingtemperature. By adjusting the power level and coil size, the inductionheating system 38 can be “tuned” to produce an ideal heated area size,to optimize the thermal forming process.

Another objective of the thermal forming process described herein isthat the material 14 should cool as quickly as possible. Since bothlaser and flame heating are relatively limited in the amount of heatthat they can transfer to the metal, neither of these heating processesare quite as good as induction heating. That is, since heat conductionis time based, the longer the heating time that is needed to reach themaximum temperature, the longer will be the time available for the heatto conduct into the surrounding metal. All of that hot metal surroundingthe primary heated area will tend to slow down the cooling rate. Incertain embodiments, it may be possible to modify the heating rate forlaser heating by increasing the power level of the laser while stillmaintaining the size of the heated region 24. The drawback is that highpower lasers can be prohibitively expensive to purchase and to maintaincompared to induction heating.

In certain embodiments, the thermal forming processes described hereinmay use exclusively induction heating for relatively thicker metalcomponents. Certain embodiments may facilitate portable use, such asdeck plate or bulkhead straightening in a shipyard. In such instances,for example, 25 kW portable induction power supplies may be used as theheat source 20. Other embodiments, in particular for forming relativelylarger plates, may use one (or multiple) 35 kW induction power suppliesas the heat source 20. In yet other embodiments, even higher capacitypower supplies and larger induction coils may be used.

It is believed that a flame torch can accomplish 13% as much bending asone induction heating head in a given amount of time. A cost comparisonfor thermal forming can be calculated assuming that the cost ofacetylene is $0.17 per cubic foot, and that the cost of electricity is$0.07 per kW-hr. Given these assumptions, for each $1.00 of operatingcost of an induction heating head, to accomplish the same amount offorming with a flame torch costs $157.37. As such, the induction heatingembodiments described herein may be considerably less expensive thancomparable flame heating embodiments.

FIG. 5 is a side view of an exemplary automated thermal forming system40 in accordance with embodiments of the present disclosure. Inaddition, FIG. 6 is another side view showing a relatively complex bendbeing formed by the automated thermal forming system 40 in accordancewith embodiments of the present disclosure. In certain embodiments, theautomated thermal forming system 40 includes a control system 86 capableof 15 degrees of freedom motion control of one or more thermal formingassemblies 88, wherein a position of each thermal forming assembly 88 isindependently controllable via positioning devices 90 (e.g., devicesthat are moveable about a thermal forming station 46, which asillustrated may include a gantry system in certain embodiments) that areattached to respective thermal forming assemblies 88 and that areindependently controllable by the control system 86.

It will be appreciated that, in certain embodiments, the control system86 includes at least one memory medium that stores computer instructionsthat may be executed by at least one processor of the control system 86to generate control signals that may be transmitted to the components ofthe thermal forming system 40 to effectuate control of operatingparameters of the thermal forming system 40. Such control signals mayinclude positioning control signals that are transmitted to thepositioning devices 90 for the purpose of controlling the positioningand/or travel speed (in both an x- and y-direction with respect to asurface 22 of the material 14 being thermally formed, as well as adistance (height) of the heating head 42 from the surface 22 of thematerial 14) of the positioning devices 90 (and, by extension, theirrespective thermal forming assemblies 88) with respect to the thermalforming station 46, heating control signals that are transmitted to thethermal forming assemblies 88 for the purpose of adjusting the amount ofheating applied (and the associated temperature generated) by thethermal forming assemblies 88, air flow and/or pressure control signalsfor the purpose of adjusting a rate of flow and/or pressure of airthrough the thermal forming assemblies 88, coolant flow and/or pressurecontrol signals for the purpose of adjusting a rate of flow and/orpressure of coolant through the thermal forming assemblies 88, and soforth.

In addition, in certain embodiments, the system 40 may include aplurality of sensors 92 (e.g., up to or exceeding 32 sensors) monitoringair flow and pressure at several locations, coolant flow and temperatureat several locations, stand-off of each of the heating heads 42 from theplate surface 22, temperature of the heated regions, sensor error fordiagnostics, and so forth, to provide feedback to the control system 86.In certain embodiments, the flexible automation system 40 has two x-axislinear motion components on each 45-foot length side 44 of the formingstation 46 and two y-axis linear motion components across a 12-footwidth heating bed 48, and six z-axis linear motion components, one forheight control of each of the thermal forming assemblies 88 (and, byextension, the heating heads 42 associated with the thermal formingassemblies 88), and two major z-axis linear motion components that movethe “head bar” 50 in the vertical direction to lower/raise the (e.g.,six, in certain embodiments) heating heads 42. All 12 motion axes areindependently controllable for each thermal forming assembly 88, or canin various combinations, be locked under software control to movesynchronously. It is noted that the system 40 has the capability tooperate up to 80 motion axes with up to 74 thermal forming assemblies 88(and, by extension, heating heads 42 associated with the thermal formingassemblies 88). In certain embodiments, two-color self-calibratingoptical temperature sensors 92 may be used to monitor the temperate ofthe heated region 24 ten times per second to insure repeatable andpredictable final plate shape. The mobile forming bed 48 may be used forrapid insertion and removal of steel plates.

The plate (e.g., material 14) shown in FIG. 5 is resting on the mobileforming bed 48. The mobile forming beds 48 operate on tracks 52—twoforming beds alternate, so that a crane can be unloading a finishedplate 14 and loading a plate 14 to be formed, while a plate 14 is in themachine being formed. This use of automatic loading enables the machineto maximize throughput. In certain embodiment, the system 40 isconfigured with six heating heads 42 but, as discussed above, thetechnology is capable of operating up to 74, or even more, heating heads42. With the 74 heating heads 42, for this application, a plate 14 canbe formed in 15 minutes or even less.

As illustrated in FIG. 5, in certain embodiments, the heating beds 48may include relatively flat surfaces upon which the plate 14 may besupported during the thermal forming process, wherein the flat surfacesdo not conform to the shape (either intermediate shape or final shape)of the plate 14 as it deforms during the thermal forming process.However, in other embodiments, the heating beds 48 may instead include adeformable liquid-filled bladder that supports the plate 14 during thethermal forming process. FIG. 9 is a side view of an exemplaryembodiment of a heating bed 48 comprising a deformable liquid-filledbladder 94 upon which plates 14 may be supported during the thermalforming processes described herein. As illustrated, as the plate 14deforms during the thermal forming process, the liquid-filled bladder 94conforms to the shape of the plate 14 throughout the thermal formingprocess. As also illustrated in FIG. 9, in certain embodiments, a layerof segmented components 96 may be disposed on top of the liquid-filledbladder 94 (e.g., between the plate 14 and the liquid-filled bladder 94during the thermal forming process. In certain embodiments, eachsegmented component 96 may be attached to adjacent segmented components96, but be capable of moving slightly with respect to each other suchthat they collectively conform to the shape of the plate 14 during thethermal forming process. In certain embodiments, the segmentedcomponents 96 may be configured to reduce heat transferred to theliquid-filled bladder 94 from the plate 14 being thermally formed. Forexample, in certain embodiments, the segmented components 96 may beceramic tiles.

In full production, to maximize the throughput, a crane (e.g., similarto the crane 12 illustrated in FIG. 1) may unload a plate 14 in no morethan approximately 7.5 minutes, and then load a new plate 14 in no morethan approximately 7.5 minutes on the first mobile forming bed 48. Then,the crane moves to the other end of the machine where the second formingbed 48 will move the currently being formed plate 14. The process ofremoving a formed plate 14 and placing a plate 14 to be formed isrepeated on the second forming bed 48, while the plate 14 on the firstforming bed 48 is moved into position and formed. This process repeatsso the machine throughput is, for example, up to four formed 10 foot by40 foot plates 14 per hour.

Returning now to FIG. 5, in certain embodiments, the control system 86downloads data from a CAD model for each plate 14, automatically plansthe forming operation, and starts the forming operation (withoutoperator intervention other than starting and monitoring the system 40,in certain embodiments) all in the time that it takes for the mobileforming bed 48 to move the plate 14 into position. After the formingoperation, height sensors on each heating head 42 become measurementsensors. The plate 14 may be scanned and the dimensions recorded for adigital quality control system of the system 40.

Each steel plate 14 that is delivered from any steel mill may vary indimensions, composition, thermo-mechanical history, and so forth. Thesevariations can cause the steel plate 14 to not react exactly as theprocess model expects. Consequently, the thermal forming system 40 iscapable of identifying any out-of-specification condition from thescanning data taken after forming. This information can be utilized bythe planning algorithm to produce a heating plan to bring the plate 14into conformance with the specification. In certain embodiments, thesensors 92 are capable of 3 mil resolution in surface heightmeasurements, and can detect relatively small variations from the CADmodel specification. In certain embodiments, the CAD model data includestolerance specifications—which the control system 86 will compare to theplate measurements, to determine if remedial forming is required tobring the plate 14 into conformance.

In certain embodiments, if a plate serial number or other identifyinginformation is on the plate 14, the control system 86 can read thatinformation (e.g., using a scanning device) and automatically downloadthe correct CAD model. Thus, the machine operator need only monitor themachine operation and be available to service the machine as may beneeded. In certain embodiments, the plates 14 may be stacked in theorder in which they are needed. Then, the crane can be automated—loadingthe mobile forming beds 48, without operator intervention, as well asunloading the plates 14 from the mobile forming beds 48. Thus, it may bepossible to only require one operator to monitor the crane and formingsystem operation. This may reduce the labor cost compared to, forexample, a large press brake 10 such as the one discussed above withrespect to FIG. 1.

All of the automated processing described above is possible because theheating heads 42 of the present embodiments are independently moveableunder control of the control system 86, rather than the plate 14 havingto move—as with a linear press brake 10 such as the one discussed abovewith respect to FIG. 1. Moving the plate 14 in a press brake 10 isrelatively slow and cumbersome. In contrast, for the embodimentsdescribed herein, once the incoming plate datum points have beenidentified, the entire forming operation is completely automated and canbe performed very rapidly. The heating heads 42 are moved to thelocations where forming is performed and, then, automatically moved tothe next forming position, based on the CAD model data.

Conventional control systems generally do not have the capabilitiesneeded for simultaneously processing the vast amount of sensor data andthen controlling 80 motion axes as described herein. The configurationof the thermal forming system 40 is such that the control system 86using a processor and software executed by the processor oversee themachine operation and provide a comprehensive operator interface. Thecontrol system 86 processes the CAD model data and, in certainembodiments, utilizes an artificial neural network process model to dothe planning of the thermal forming. Then, the DSP-based controllerreceives the heating plan, and executes that plan. In certainembodiments, the control system 86, with the full 74 heating heads 42,may process over 10 megabytes of sensor data per second, in order tomonitor the process and the machine health. In certain embodiments, thecontrol system 86 may utilize a modified version of S.H.I.E.L.D., amonitoring system co-developed by EnergynTech, Inc. personnel andCaterpillar Corporation with funding from the National Institute ofStandards and Technology—Advanced Technology Program (NIST-ATP).S.H.I.E.L.D. was designed to process data from over 100 sensors (e.g.,the sensors 92 described herein) embedded in a large mobile structure,monitor the fatigue damage, and calculate remaining structure life, insubstantially real-time. The software developed for S.H.I.E.L.D. by theEnergynTech team, was modified to be able to monitor the large volume ofsensor data from the system 40, also in substantially real-time.

One primary drawback is that thermal forming is relatively slow comparedto mechanical forming methods except when producing three-dimensionalshapes, which are relatively difficult to produce using mechanicalbending. In certain embodiments, to increase the speed of the system 40,a heated line may be used, rather than moving a heated spot along aline, to deform the metal. In other words, the thermal formingassemblies 88 may be configured such that a line extending an entirelength (or at least a substantial portion of a length) of the plate 14may be simultaneously heated. This heated line method may result in asignificant increase in the speed of thermal forming in an embodiment inwhich a laser beam is optically converted to a line. Mechanical bendingmay generally be faster than a line heating method of thermal formingfor relatively thick metal parts. There is a need, therefore, for aheated line bending method that has sufficient power to be used on thickmetal parts.

The embodiments described herein address these drawbacks by providing athermal forming method that uses relatively high power induction heatingto create an equivalent heated line to be able to produce forming orbending rapidly in relatively thick metal parts. The technique may makeuse of one or more induction heating power supplies, such as the heatsource 20 (e.g., the heating heads 42) of the thermal forming system 40to produce more power than a typical flame or laser, and that may thusbe able to perform the thermal forming process by generating anequivalent of a heated line that will bend or form relatively thickmetal much more rapidly. The embodiments described herein alsocontemplate control of the cooling of the metal part in order to removethe heat rapidly enough so that the significant thermal gradient willexist in the metal part that is required for the thermal formingprocess.

In contrast to a line heating approach (e.g., FIG. 7A), where a heatedspot 54 is moved along a line path 56, as illustrated by arrow 58, andthen multiple adjacent line paths 56 are used to produce a bend in themetal part 14, this method (e.g., FIG. 7B) generates a single heatedline 60 and the heated line may be moved (e.g., perpendicular to) adirection of the heated line 60, as illustrated by arrow 62, to create abend in the metal part 14. In certain embodiments, the heated line 60may be produced by a single heating element, such as an induction coilthat has a relatively large power source, or by a series of smallerinduction coils arranged in a line or moved along a line which togetherconstitute the equivalent of a heated line 60. A single cooling systemor multiple smaller cooling systems may be used to cool the metal part14 as the heated line 60 is moved across the plate surface.

One disadvantage of the line heating method (e.g., FIG. 7A) is that theheated spot 54 is working to bend the plate 14 at a single location, butthe remainder of the metal along the path 56 is not being activelyformed or bent and, therefore, becomes an impediment to the forming orbending. By using an entire heated line 60 (e.g., FIG. 7B), all parts ofthe heated line 60 are being simultaneously formed and a cooperativebending or forming takes place. This results in a significant increasein the rate of forming, which can exceed a factor of 100 fold increasein the rate of forming of a metal part 14, in comparison to conventionalmethods.

The plan for line heating that is implemented by the control system 86includes the line paths 56 along which a heated spot 54 will traverse(in the case of the line heating method of FIG. 7A) or the line path ofthe heated line 60 (in the case of the heated line method of FIG. 7B),the amount of heat applied by each heating head 42, the number of passesof the heated spot 54 that will be made along each portion of the pathof the line (in the case of the line heating method of FIG. 7A), and soforth. Generally, the planning systems for this process utilize datafrom computer aided design and computer aided manufacturing (CAD/CAM)systems, which may provide the control system 86 with the plans forexecution, and which may also describe the shape of the part (e.g., ametal plate 14) that is to be formed.

In certain embodiments, a single heating head 42 (e.g., associated witha single induction coil, in certain embodiments) may be used to generatethe heated line 60. In other words, in certain embodiments, a heatinghead 42 of an individual thermal forming assembly 88 may be shaped insuch a way that an entire line of the material 14 may be simultaneouslyheated. It will be appreciated that, in such an embodiment, the powerlevel of the applied energy will need to be increased as the length ofthe induction coil increases. In other embodiments, multiple inductioncoils may be used with individually lower power levels, but an aggregatehigh power level commensurate with the length of the line 60 and themetal alloy that is being formed. In such an embodiment where multipleinduction coils are used, the thermal forming assemblies 88 associatedwith the multiple induction coils may be positioned by the controlsystem 86 such that they are aligned appropriately with respect to theline 60.

In certain embodiments, the height of the induction coil may becontrolled by the control system 86 using sensor feedback from thesensors 92 to guide the positioning. Because water cooling is generallyused, as described below, in certain situations, the water may at leastpartially interfere with direct measurement using a laser height sensor92 due to reflection of the laser light being misdirected by the watersurface. In such embodiments, a mechanical device may be used to measurethe height of the induction coil with respect to the surface 22 of thematerial 14. As described below, in certain embodiments, a circular airknife will be used. In such an embodiment, a laser height sensor 92 maybe used to measure the height of the induction coil with respect to thesurface 22 of the material 14 being thermally formed. The dry areacreated by the circular air knife minimizes the risk of erroneousmeasurements and provides a stable data feedback to the control system86. In certain embodiments, an infrared temperature sensor 92 may alsobe used to control the power being delivered to the induction coil, suchthat a correct maximum temperature is maintained relatively uniformthroughout the thermal forming process. In such an embodiment, thecircular air knife keeps the spot under the induction coil dry andclean, such that the infrared sensor 92 does not generate erroneous dataoutput due to water or debris on the surface 22 of the material beingthermally formed.

In certain embodiments, multiple induction coils (e.g., associated withmultiple thermal forming assemblies 88) may be used, and the height ofeach respective induction coil with respect to the surface 22 of thematerial 14 being thermally formed may be individually controlled by thecontrol system 86. The use of multiple induction coils to from theheated line 60 provides the ability of the heated line forming system tohave each of the induction coils at any given location (and relativeheight) with respect to the surface 22 of the material 14 beingthermally formed, which makes accurate forming of the material 14 (evenhaving an initial curved topography) possible. Multiple induction coilsalong the heated line 60 provides the automated thermal forming system40 with the ability to change the shape of the surface topography of theheated line 60 as the shape of the material 14 changes during thethermal forming process.

Although described herein as primarily involving moving a heated spot 54along a linear path 56 or using an entire heated line 60, in otherembodiments, the pattern that the heated spots 54 are moved, or thepattern that the heated “line” forms, may not be a line at all, butrather may be any curvilinear pattern in any or all of the axesmentioned above. For example, in certain embodiments, a heated spot 54may be moved in any curvilinear pattern in a direction parallel to theplane 30 of the heated material 14 and/or a direction perpendicular tothis plane 30 (e.g., toward or away from the heated material 14 in thethrough-thickness direction 28 and/or along a length of the heatedmaterial 14). Similarly, the layout of a plurality of heating heads 42may be such that instead of a heated line 60 that is moved by the system40, a heated curvilinear pattern of heating heads 42 may be moved by thesystem 40. Such non-linear heating patterns may prove advantageous, forexample, in pipe forming, I-beam forming, plate forming when a waved orother complex three-dimensional pattern is desired, and so forth. It isnoted that such non-linear thermal forming techniques provide distinctadvantages over conventional mechanical bending techniques, which maynot even be capable of providing such complex three-dimensional bends.

As discussed above, the constraint of the cooler metal surrounding theheated metal contributes to the proper functioning of the thermalforming process. In order to maintain a relatively large thermalgradient needed to keep the surrounding metal from heating, the processis made more efficient and faster the colder the surrounding metal is.In certain embodiments, cooling may be accomplished by convection ofheat from the metal surface, or by applying a spray of water on thesurrounding metal. One drawback to this approach is that the water mayintrude to the heated spot 54 or heated line 60, thereby reducing theamount of heat available, which reduces the rate of heating. Inaddition, if the water is not sprayed onto the metal surface, then afilm of warm liquid forms on the metal surface, which reduces thecooling efficiency and, therefore, reduces the forming efficiency and,thus, the forming rate. However, spraying the water on the surface withsufficient force to continually remove the film of warm water adjacentto the surface, may cause water to splash onto the heated spot 54 orheated line 60.

One method of cooling is to combine a pressurized water spray onto thesurface with an air-knife which generates a barrier between the cooledmetal surface and the heated metal surface, and prevents water fromsplashing onto the heated region. In the case of a heated spot 54, acircular air knife may be created around the heated spot 54. If thecircular air knife is made in a frustoconical shape so that the narrowerend of the frustoconical shape is closest to the metal surface, then theconvergence of the air on the metal surface generates a region ofelevated air pressure. The elevated air pressure causes the air to moveaway from the heated spot 54, preventing air turbulence from drawingsome of the water into the heated area of the metal surface. Only anarrow range of cone angles may be used for the frustoconical shape ofthe circular air knife. If the cone angle is too large, then the flow ofair from the air knife will overcome the slight pressure differentialand water may be drawn from the plate surface to the heated area of thesurface. If the cone angle is too small, then the air knife will notgenerate a sufficient increase in local pressure inside the circular airknife and the turbulence at the surface of the metal will draw waterinto the heated area of the surface. In certain embodiments, instead ofan air knife, a physical bather may be used, and which may not extenddown to the surface 22 of the material 14 being thermally formed, butdoes act as a barrier to, for example, the escape of laser lightreflected from the surface, when lasers are used as the heat sources 20.

The frustoconical circular air knife is generated by forming afrustoconical air guide with a smooth surface. FIG. 8 is across-sectional side view of an exemplary thermal forming system 40 inaccordance with embodiments of the present disclosure. Surrounding thefrustoconical air guide 64 is a circular air delivery device 66, whichis constructed such that air 68 is delivered by an internal passage 70that starts the air 68 on a downward path, then diverts the air flowradially inward toward the center of the frustoconical air guide 64, asillustrated by arrows 72. At the opening adjacent to the frustoconicalair guide 64, the air delivery device passage 70 narrows and forms anair sheet which develops lamellar flow that conforms to a curved surfacethat the lamellar air sheet follows. The curvature of the surface endsat the same angle of flow as the corresponding frustoconical air guide64 such that the lamellar sheet of flowing air 68 then transfers to, andfollows, the surface of the frustoconical air guide 64 down to thesurface 22 of the metal part 14 being formed. The frustoconical airguide 64 surrounds the heating coil 74 which is held adjacent to themetal part 14 being bent or formed, forming a heated area on the platejust below the coil 74. The water spray follows the path illustrated byarrows 76, 78 down to the metal part surface 22, then is directed awayfrom the heated area on the metal part 14 by the air flow illustrated byarrows 80, 82, 84. It should be noted that, although described herein asusing water, other coolants (e.g., liquified gases such as liquid argon,solidified gases such as carbon dioxide snow, and so forth) may be usedinstead of water, especially to increase the cooling rate of metals thatmay be reactive to water.

For the situation of a heated line 60, not made up of multiple heatedspots 54, but instead with a single continuous coil 74, the design maybe similar to that illustrated in FIG. 8, except that the cross-sectionis of a long linear air knife, rather than a circular air knife. Forexample, the sides of the air guide 64 would be planar rather thanfrustoconical circular. Otherwise, the design would have a substantiallysimilar cross-sectional profile.

In other embodiments, a plurality of thermal forming assemblies 88 withrespective heating heads 42 (e.g., induction coils) may be used togetherand positioned appropriately along the heated line 60. In such anembodiment, the air guides 64 for the thermal forming assemblies 88 may,for example, include two substantially parallel walls 98 disposed onopposite sides of the respective heating head 42, and the control system86 may position the thermal forming assemblies 88 such that the walls 98of the thermal forming assemblies 88 generally align parallel with eachother such that the air guides 64 of the thermal forming assemblies 88provide the same functionality as a long linear air knife, as describedabove. FIG. 10 is a cutaway top view of such an embodiment.

While only certain features of the invention have been illustrated anddescribed herein, many modifications and changes will occur to thoseskilled in the art. It is, therefore, to be understood that the appendedclaims are intended to cover all such modifications and changes as fallwithin the true spirit of the invention.

The invention claimed is:
 1. A heated line forming system comprising: aheating coil system comprising a plurality of induction heating coilsconfigured to produce a heated line on a surface of a metal plate and tomove the heated line relative to the surface of the metal plate during athermal forming process, wherein an entire length of the heated line isheated simultaneously by the plurality of induction heating coils; andan air knife cooling system configured to: direct airflow to maintain adry area for the heated line during the thermal forming process; anddirect a fluid coolant around the heated line via a spray mechanism suchthat the fluid coolant is blocked by the airflow from flowing onto theheated line on the surface of the metal plate during the thermal formingprocess.
 2. The heated line forming system of claim 1, wherein the airknife cooling system comprises a respective air knife for each of theplurality of induction heating coils.
 3. The heated line forming systemof claim 1, wherein the plurality of induction heating coils areindependently positionable with respect to a support structure by anautomated control system.
 4. The heated line forming system of claim 1,comprising at least one flat surface upon which the metal plate issupported during the thermal forming process, wherein the at least oneflat surface does not conform to a final metal plate shape or anintermediate metal plate shape during the thermal forming process. 5.The heated line forming system of claim 1, comprising a liquid-filledbladder, wherein the metal plate is supported by the liquid-filledbladder during the thermal forming process, wherein the liquid-filledbladder conforms to a final metal plate shape or an intermediate metalplate shape during the thermal forming process.
 6. The heated lineforming system of claim 5, comprising a layer of segmented componentsdisposed between the liquid-filled bladder and the metal plate duringthe thermal forming process, wherein the layer of segmented componentsis configured to reduce heat transferred to the liquid-filled bladderfrom the metal plate during the thermal forming process.
 7. The heatedline forming system of claim 6, wherein the segmented componentscomprise ceramic tiles.
 8. The heated line forming system of claim 1,wherein a plurality of heated spots along the heated line are heatedsimultaneously.
 9. The heated line forming system of claim 1, whereinthe airflow is directed to a guide configured to generate an air barrierbetween the fluid coolant and the heated line.
 10. A heated line formingsystem comprising: a plurality of induction heating coils configured toproduce a heated line on a surface of a metal plate and to move theheated line relative to the surface of the metal plate during a thermalforming process, wherein an entire length of the heated line is heatedsimultaneously by the plurality of induction heating coils during afirst portion of the thermal forming process; and a control systemconfigured to control each of the plurality of induction heating coilsindependently during a second portion of the thermal forming process tochange a heating profile of the heated line as the plurality ofinduction heating coils moves relative to the surface of the metalplate.
 11. The heated line forming system of claim 10, wherein thecontrol system is configured to independently control at least oneoperating parameter of each of the plurality of induction heating coilsbased at least in part on operating data detected by one or more sensorsof the heated line forming system.
 12. The heated line forming system ofclaim 11, wherein the at least one operating parameter comprises anamount of bending of the metal plate, a temperature generated by arespective induction heating coil, a distance of a respective inductionheating coil from a surface of the metal plate, a travel speed of arespective induction heating coil with respect to the metal plate, aposition of a respective induction heating coil with respect to themetal plate, or any combination thereof.
 13. The heated line formingsystem of claim 10, comprising an air knife cooling system configured tomaintain a dry area for the heated line, and to direct coolant aroundthe heated line via a spray mechanism such that the coolant is blockedfrom flowing onto the heated line on the surface of the metal plateduring the thermal forming process.
 14. The heated line forming systemof claim 13, wherein the air knife cooling system comprises a respectiveair knife for each of the plurality of induction heating coils.
 15. Theheated line forming system of claim 10, wherein the plurality ofinduction heating coils are independently positionable with respect to asupport structure of the heated line forming system by the controlsystem.
 16. The heated line forming system of claim 10, wherein themetal plate comprises a substantially flat metal plate.
 17. The heatedline forming system of claim 10, wherein the metal plate is a curvedmetal plate.
 18. The heated line forming system of claim 10, comprisingat least one flat surface upon which the metal plate is supported duringthe thermal forming process, wherein the flat surface does not conformto a final metal plate shape or an intermediate metal plate shape duringthe thermal forming process.
 19. The heated line forming system of claim10, comprising a liquid-filled bladder, wherein the metal plate issupported by the liquid-filled bladder during the thermal formingprocess, wherein the liquid-filled bladder conforms to a final metalplate shape or an intermediate metal plate shape during the thermalforming process.
 20. The heated line forming system of claim 19,comprising a layer of segmented components disposed between theliquid-filled bladder and the metal plate during the thermal formingprocess, wherein the layer of segmented components is configured toreduce heat transferred to the liquid-filled bladder from the metalplate during the thermal forming process.
 21. The heated line formingsystem of claim 20, wherein the segmented components comprise ceramictiles.
 22. A heated line forming system comprising: a plurality ofinduction heating coils configured to produce a heated line on a surfaceof a metal plate during a thermal forming process; a control systemconfigured to control each of the plurality of induction heating coilsindependently during the thermal forming process; and a layer ofsegmented components disposed between a liquid-filled bladder and themetal plate during the thermal forming process, the layer of segmentedcomponents configured to reduce heat transferred to the liquid-filledbladder from the metal plate during the thermal forming process.